One important service provided by a group server connected to a Public Land Mobile Network (PLMN) is that of automatically establishing group calls. A group call is a conference call in which all participants can in turn talk and listen to each other, or, alternately, a broadcast call in which all the participants simultaneously receive a transmitted message. Another important service which is starting to be provided in PLMNs is that of voice mail. This service allows a mobile subscriber to, instead of immediately receiving a telephone call from a calling party, forward the call to a voice mail system which will then offer the calling party an opportunity to leave a voice mail message, which is then stored and later retrieved by the mobile subscriber. A problem may develop in the interaction of these two services, in that, during the process of setting up a group call, one of the mobile stations may have the call forward feature set so that all of its calls are forwarded to a voice mail system. In this case, a connection for the call will be made to the voice mail system which will then produce a voice mail announcement. Thus, a connection will not be established to the intended mobile station, and if nothing is done further to correct this unintended action, the automated group controller will connect the voice mail system to the group call.
In the related art, there are several solutions which have been proposed to solve this problem. Each of the solutions has corresponding disadvantages. One proposed solution is to permanently switch off the call forward service for all subscribers that may be part of a group call. However, this would preclude these subscribers from using the call forward feature. Since the call forward feature is a standard feature in PLMNs, this is not a desirable solution.
Another proposed solution is to provide a mobile subscriber with dual subscriptions, i.e. a subscription exclusively dedicated to group calls and a regular subscription for all other calls. The group call subscription would have call forward service permanently disabled. The regular subscription would allow the call forward service. Although dual subscriptions appears to be a good solution, this solution may cause conflict with fraud detection systems in the network since the mobile equipment can change subscriptions very quickly.
In yet another proposed solution, it is possible for the automated group controller to switch off the call forward service for the terminating parties, i.e. the parties to be added to the group call. In this approach, the automated group controller accesses the home location register (HLR) to determine if the called party is detached or otherwise unreachable. The automated group controller may then switch off the call forward service of the called party. However, there are problems with this approach. First, an interface will have to be developed exclusively to enable this interaction between the automated group controller and the HLR. Then there is the security problem of providing HLR information to the automated group controller. There is also a problem if someone else calls the terminating party after the call forward service has been switched off. There is also a problem if the automated group controller fails to reset the changes in the HLR. Additional problems result in handling additional call forward services, such as call forward on no reply and call forward on busy.
In yet another proposed solution, the automated group controller detects a backward notification of the call forward service and only adds those parties that have not enabled the call forward feature. Backward notification only works for an automated group controller using the Integrated Services Digital Network User Part (ISUP) of some versions of the Global Systems For Mobile Communications (GSM). In these versions of GSM, a backward notification signal is sent to the automated group controller indicating that a call forward service is in progress, e.g., Advance Mobile Phone Service (AMPS) networks do not support backward notification of a call forward service.
In view of the foregoing, it would be desirable to provide one or more techniques which overcomes the above-described inadequacies and shortcomings of the above-described proposed solutions.